Typically, a Maximum Brake Torque (MBT) timing of an internal combustion engine is determined by conducting a spark sweep of an engine. By industry standards, a spark angle at maximum torque is referred as the MBT. A typical calibration point needs a spark sweep or mapping to see if the engine is operated at a desirable MBT timing condition. Spark mapping usually requires a tremendous amount of effort and time to achieve a satisfactory calibration. In recent years, various MBT timing detection schemes have been proposed based upon in-cylinder pressure or spark plug ionization signal.
Environmental and fuel economy issues have recently driven trends towards improved the efficiency of combustion engines. Typical trends have sought use of feedback control directly from the combustion information instead of using indirect measurements. Common availability of computing power has revolutionized possibilities of sensor interpretation and closed loop feedback control. Recent control developments are usually based on new sensors or improved interpretations of available sensor signals. One example is ionization current sensing which is obtained by applying a bias voltage on the spark plug when it is not used for ignition. The sensed ionization current typically depends on the ions created, and on correspondingly relevant ion factors (such as their relative concentration and recombination), on pressure, and on temperature. The ionization signal is typically rich in combustion information, but may also be complex to analyze.
The ionization current is typically measured at a low-voltage side of the secondary winding of an ignition coil and may not require protection from high-voltage pulses in the ignition. Examples of ionization current measurement systems are already in use for analyses of individual cylinder knock control, cam phase sensing, pre-ignition detection, misfire detection, and combustion quality detection such as dilution and lean limit. In addition, detection techniques of spark plug fouling by using the ionization current have been dessiminated throughout the industry.
Prior techniques have used ionization current data in an engine cylinder immediately after ignition and compared the data against a reference data to provide a correction control when a result of the data comparison indicates a less than desirable internal combustion, i.e. low output power or degradation in the cylinder combustion. Conventional techniques have typically collected only discrete and/or periodical data, such as peak of signals, during an engine cylinder operation for inputs in corresponding feedback control schemes. It has been found that when the engine is operated at the corresponding MBT timing, a peak cylinder pressure usually occurs around 15° ATDC (After Top Dead Center), and the 50 percent Mass Fraction Burned (MBF) location generally occurs from 8° to 10° ATDC.
In view of the above-discussed problems, it is an object of this invention to provide a real-time estimation algorithm using an ionization signal to construct a composite MBT timing criterion, which is robust over an engine operational map. Accordingly, this invention discloses a real-time estimation algorithm, using both analog and digitally conditioned ionization signals, to construct a composite MBT timing criterion that is robust over an engine operational map.
One advantageous feature of this invention is the providing of a composite MBT timing criterion based upon the shape of ionization signal, instead of magnitude for improved estimation robustness.
Another advantageous feature of this invention is the providing of a mixed signal conditioning method, which includes both analog signal and digital signal conditioning, for improved estimation quality. The analog signal conditioning circuit may reduce both ionization signal sample rate and the microprocessor throughput of digital signal conditioning. In addition, the composite MBT timing criterion may utilize multiple MBT timing measures of the ionization signal to generate a true full range MBT timing criterion. As a result, a real-time estimation algorithm, using ionization signals, to construct a composite MBT timing criterion that is robust over engine operational map is realized.